1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a transflective liquid crystal display (LCD) device.
2. Discussion of the Related Art
Flat panel display (FPD) devices that are small, lightweight, and have low power consumption have been a subject of recent research in the advent of the information age. FPD devices may be classified into two types depending on whether the device emits or receives light. One type is a light-emitting type display device that emits light to display images, and the other type is a light-receiving type display device that uses an external light source to display images. Plasma display panels (PDPs), field emission display (FED) devices, and electroluminescent (EL) devices are examples of the light-emitting type display devices. Liquid crystal display (LCD) devices are examples of the light-receiving type display device. Among many kinds of FPD devices, LCD devices are widely used for notebook computers and desktop monitors because of their excellent characteristics of resolution, color display and display quality.
Generally, LCD devices include an upper substrate and a lower substrate facing each other with liquid crystal molecules interposed therebetween. Each substrate has an electrode on the inner surface thereof. An electric field is generated by applying a voltage to the electrodes, thereby driving the liquid crystal molecules to display images in accordance with the light transmittance.
Since LCD devices do not emit light, an additional light source is necessary. Accordingly, LCD devices display images by disposing a backlight at a backside thereof and transmitting light from the backlight. Here, electric field-generating electrodes of the LCD devices are made of a transparent conductive material and the two substrates are transparent. This kind of LCD device is referred to as a transmission type LCD device or a transmissive LCD device. Even though a transmissive LCD device can display bright images under a dark environment due to an artificial light source such as a backlight, the transmissive LCD device has a disadvantage of high power consumption due to the backlight.
To remedy this disadvantage, a reflective (or reflection type) LCD device is suggested. The reflective LCD device displays images by reflecting external natural or artificial light, thereby having a low power consumption compared with the transmissive LCD device. In the reflective LCD device, a lower electric field-generating electrode is made of a conductive material having high reflectance and an upper electric field-generating electrode is made of a transparent conductive material so that external light can be transmitted through the upper electric field-generating electrode.
The reflective LCD device has much lower power consumption than the transmissive LCD device. However, the reflective LCD device cannot be used in dark places because it depends on an external light source.
Therefore, a transflective LCD device, which can be used both in a transmissive mode and in a reflective mode, has been recently proposed. A transflective LCD device of the related art will be described hereinafter more in detail.
FIG. 1 is a plan view of an array substrate for a transflective LCD device according to the related art.
In a transflective LCD device 1 of FIG. 1, a plurality of gate lines 3 is horizontally extended and a plurality of data lines 20 is vertically formed in the context of the figure. The gate and data lines 3 and 20 cross each other to define a pixel P. A thin film transistor T, which includes a gate electrode, a semiconductor layer, a source electrode and a drain electrode, is formed at each crossing of the gate and data lines 3 and 20.
In the pixel P, a transmissive area TA in the middle of the pixel P and a reflective area RA around the transmissive area TA are defined. To improve brightness and color properties of the transmissive and reflective modes, a transmissive hole TH is formed to create the transmissive area TA, so that cell gaps may be different in the transmissive area TA and the reflective area RA.
FIG. 2 is a cross-sectional view along the line II-II of FIG. 1. As shown in FIG. 2, a gate electrode 6 is formed on a transparent substrate 1 and a gate insulating layer 10 is formed on the gate electrode 6. A gate line (not shown) connected to the gate electrode 6 is formed under the gate insulating layer 10. An active layer 13 and an ohmic contact layer 16a and 16b are sequentially formed on the gate insulating layer 10 over the gate electrode 6. A source electrode 23 and a drain electrode 26 are formed on the ohmic contact layer 16a and 16b. The source and drain electrodes 23 and 26 with the gate electrode 6 form a thin film transistor T. A data line 20 made of the source and drain electrodes 23 and 26 is formed on the gate insulating layer 10. Although not shown in the figure, the data line 20 is connected to the source electrode 23. The data line 20 crosses the gate line to define a pixel region SP.
A first passivation layer 30 is formed on the thin film transistor T and the data line 20. The first passivation layer 30 is made of an organic material having relatively low dielectric constant. The first passivation layer 30 is removed in the transmissive area TA to create the transmissive hole TH, and remains in a reflective area RA.
A reflector 40 is formed on the first passivation layer 30 in the reflective area RA. The reflector 40 is made of a metallic material that reflects light well. The reflector 40 has a flat surface. A second passivation layer 45 is formed on the reflector 40 and the gate insulating layer 10 exposed in the transmissive area TA. The second passivation layer 45 is made of an inorganic material. The second passivation layer 45 and the first passivation layer 30 over the drain electrode 26 of the thin film transistor T are etched to form a drain contact hole 55 exposing the drain electrode 26. A pixel electrode 50 is formed on the second passivation layer 45 in the pixel region SP. The pixel electrode 50 is connected to the drain electrode 26 through the drain contact hole 55.
However, glare occurs in the transflective LCD device. This happens when a high-intensity external light source is reflected on a liquid crystal display panel. The displayed image is poor due to the glare that occurs as viewed by an observer due to the reflection of light. Therefore, a reflector of an uneven shape is used to increase the brightness along the normal direction and to decrease the glare.
FIG. 3 is a cross-sectional view of another array substrate for a transflective LCD device according to the related art. The array substrate of FIG. 3 has the same structure as that of FIG. 2 except for the reflector. In FIG. 3, the reflector 41 has an uneven surface due to the unevenness of the first passivation layer 30. The uneven surface of the reflector 41 results in diffused reflection of incident light minimizing specular reflection. Accordingly, a brightness along a normal direction of the transflective LCD device in the reflective mode increases by changing a reflection angle of light.
The transflective LCD device including the array substrate of FIG. 3 has good color properties.
Recently, the variety of mobile phones and personal digital assistants (PDAs) using the transflective LCD device have increased, and devices of high resolution are required. An LCD device having a high resolution of about 300 ppi (pixel per inch) includes pixels of about 84 μm×28 μm. Here, both reflective and transmissive areas are defined in each pixel and abut each other. However, the transmissive hole forms a step in the reflective area and the uneven reflector in the reflective area extends to the transmissive area along sidewalls of the transmissive hole. Such an arrangement causes problems in the manufacturing processes, for example, metallization at the edge of the step as well as maintaining unevenness of the reflector thereby obtaining good reflective properties. In addition, since the transmissive hole is small, an alignment layer (not shown) for aligning the liquid crystal molecules in the liquid crystal layer may be poorly rubbed in a rubbing process performed after the alignment layer is provided on pixel electrode in the transmissive and reflective areas. Accordingly, transmissive properties may be lowered.